1. Field of the Invention
The present invention relates to lasers which are tunable over a broadband of frequencies. Lasers having a broad gain linewidth may be forced to lase in a narrow line by the insertion of a frequency selective element in the laser cavity. If the bandpass of this element is adjustable, the laser output frequency may be tuned over the gain linewidth.
2. Description of Prior Art
Some commonly used earlier tuning means include mechanically rotable gratings, tiltable or piezo electrically driven etalons, or adjustable prisms. These methods tend to be slow and are subject to hysteresis and resettability problems. This disclosure describes a nonmechanical tuning technique that can eliminate these problems and is potentially capable of very high frequency operation. The present invention contemplates the use of electronic tuning.
Prior work has been done on electrically tunable filters by such as Messieurs Taylor, Harris and Nich and Hansch, whose findings were reported in Applied Phycis Letters, Volume 19, No. 8, of 15 Oct. 1971, under the title "electronic Tuning of a Dye Laser Using the Acousto-Optic Filter." The work described therein contributes to the foundation of knowledge upon which the present invention rests. Tuning was achieved therein by applying an RF signal to an acousto-optic filter utilizing a collinear interaction between an ordinary optical wave, an extra-ordinary optical wave, and a travelling acoustical wave in a birefringent crystal. Although the optical frequency to which the laser is tuned is not equal to the acoustic frequency applied to the crystal, they must satisfy a particular relationship with one another. Only the corresponding optical frequency undergoes a 90.degree. polarizing rotation to be provided as the output. All other optical frequencies are effectively blocked. That is, the RF frequency applied causes the corresponding optical frequency to undergo a 90.degree. polarization rotation, which polarized frequency is the one transmitted by the filter and provided as the tuned output of the laser. All other frequencies are not related and are therefore, blocked by the filter.